1. Field of the Invention
The present invention relates generally to intervertebral discs and vertebrae and methods of hypothermia therapy applied thereto to relieve pain and restore function.
2. Description of the Related Art
Low back pain afflicts more than 10 million people in the United States annually. It impacts the individual sufferer""s life physically, emotionally and financially, restricting his or her activities and often leading to depression and absenteeism from work. As a nation, the United States spends more than $50 billion dollars in direct and indirect medical expenses related to back pain, making it one of the leading healthcare expenditures overall.
The intervertebral disc consists of the annulus fibrosus, nucleus pulposus, and the endplates of the superior and inferior vertebral bodies. The annulus and endplates contain the nucleus as the disc is pressurized during normal activities. The posterior annulus is thinner in cross-section than the anterior annulus and is correspondingly the site most frequently affected by injury.
Deterioration of the structure of the intervertebral disc is one of the leading causes of low back pain. The intervertebral disc is formed from a tough, outer annulus fibrosus surrounding a softer, gelatinous nucleus pulposus. The annular fibers attach securely to the endplates of the vertebral bodies superiorly and inferiorly, trapping the nucleus and creating an isobaric environment. As load is applied through the spinal column, pressure within the nucleus increases and is distributed across the vertebral endplates and annulus. These structures flex and strain until the spinal load is equilibrated by intradiscal pressure allowing the disc to act as a xe2x80x9cshock absorberxe2x80x9d. Lack of significant vascularity in the annulus and nucleus limits their healing potential.
Small nerve endings penetrate the outer annulus. As a person ages, rents in the inner or central layers of the annulus can create focal regions of high pressure in the outer annulus that mechanically stimulates these nerve endings resulting in pain. There is also an increasing body of evidence suggesting an inflammatory response in and around nerves within the annulus and within the epidural space behind the disc induced by chemicals within the nucleus, vertebral endplates, and vertebral bodies. Passage of these chemicals through the annulus can also occur because of damage to the annulus through physical trauma, progressive aging, or degenerative disc disease. Under normal loading, portions of the nucleus or its degenerative byproducts may be forced into and through rents in the annulus, such chemicals are thought to be transported into proximity with these sensitive nerves resulting in inflammation and pain.
Therapeutic methods involving decreasing the temperature of the body or tissues thereof have a long history in medicine. Cold has been used successfully to bring about localized tissue necrosis, for cryoblation of tissue, as an anesthetic, and as a technique for inducing angiogenesis as a part of an overall healing response to the cold injury. Cryotherapy can be defined as the therapeutic use of cold and is not limited by any particular range of temperatures. Cryosurgery or cryocautery is usually more narrowly defined not merely as the use of cold in surgical applications but as the technique of exposing tissue to extreme cold in order to produce well demarcated areas of cell injury and destruction. Cryosurgical temperatures are typically below xe2x88x9220xc2x0 C. On the other hand, hypothermia therapy involves a technique of lowering body or tissues thereof below body temperature, usually between 26xc2x0 C.-32.5xc2x0 C. Cryosurgery is distinguishable from the other two methods in that tissue is cut or ablated or otherwise destroyed with precision whereas cyrotherapy and hypothermia therapy techniques utilize cold or extreme cold to improve the health of tissue through stimulation. Accordingly, for purposes of this disclosure, hypothermia therapy includes cryotherapy or the therapeutic use of cold and extremely cold temperatures well below normal body temperature. Also, to the extent that related instrumentation such as hypothermia needles, cryogenic catheters, and cryoprobes (flexible or rigid) can be used to apply cryoenergy or cool tissue to a broad range of temperatures below normal body temperature, use of a specific type of instrument in a method of the invention disclosed herein does not necessarily imply a certain range of therapeutic temperatures. For instance, cryoprobes and cryocatheters may be used interchangeably according to various embodiments of the present invention.
Various embodiments of the present invention relate to devices and methods for treating the tissue in and around the intervertebral disc through localized hypothermia therapy to reduce pain or restore function in the disc and surrounding tissue. Hypothermia therapy is defined as the reduction of tissue temperature to below that of the equilibrium temperature. Target therapeutic temperature ranges from about xe2x88x92272xc2x0 C.-37xc2x0 C. for at least one period of up to about an hour depending upon the desired treatment effect.
According to various methods of the invention, hypothermia therapy of the intervertebral disc and adjacent vertebral bodies may be used to reduce painful pathological states of the spine. Various embodiments of the disclosed method may involve exposure of tissues including the annulus fibrosus, nucleus pulposus, and adjacent vertebral bodies including their respective nerve fibers to a range of low temperatures over a period of time. Depending on the temperatures and exposure time, this can lead to structural or chemical denaturation of tissue including selective cell death and cryoblation. The therapy may also involve temporary or permanent deadening of the nerves within or surrounding the disc. Also, hypothermia therapy may be used for the induction of a healing response, angiogenesis, or accelerated degeneration and/or drying of the nucleus pulposus and/or annulus fibrosus. Various effects can be achieved by reaching different temperatures for differing periods of time or by the proximity of the hypothermia therapy device to the treatment target. Accordingly, it is an object of one or more the embodiments of the invention to provide hypothermia therapy to selected locations within an intervertebral disc.
In one or more embodiments of the invention, the therapy may be delivered via a flexible, elongated catheter, by a flexible or rigid probe, or by a cooling element extending along at least a portion of a length of an articulated segment of a therapy delivery probe. The devices may be delivered through an open surgical approach or via percutaneous approaches to the intervertebral disc and surrounding structures.
Various embodiments of the invention may be practiced with a cryoprobe having a blunt tip or a retractable blunt or curved tip surface capable of deflecting off of the annular surface as the probe is advanced into the disc or along the surface of an annular lamella. Such a tip may also be used to deflect off of a vertebral endplate or the interior surface of a vertebral body.
The method of applying hypothermia to the disc may be accompanied by concurrent measurement of the local tissue temperature. This may be done through the use of thermocouples in the probe itself or by the use of secondary devices positioned within the tissues in or around the disc capable of temperature measurement. The region of therapy may also be monitored non-invasively through the use of ultrasound or comparable imaging technique capable of identifying the formation and extent of ice within living tissue. This technique is commonly referred to as cryomapping.